The present exemplary embodiment relates generally to a printing system comprising at least two marking engines and more particularly to a printing system which allows automated modification of the xerographic subsystems in at least one of the at least two marking engines to accommodate a different print media substrate than that normally used.
In a typical xerographic marking engine, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto the paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure.
A common trend in the maintenance of office equipment, particularly copiers and printers, is to organize the machine on a modular basis, wherein certain distinct subsystems of a machine are bundled together into modules which can be readily removed from machines and replaced with new modules of the same type. A modular design facilitates a greater flexibility in terms of replacement and repair, which can take place at a remote location.
Printing systems which incorporate several small marking engines have recently been developed, as described for example, in the above-referenced co-pending applications. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple marking engines. Such systems are commonly referred to as “tandem engine” printers, “parallel” printers, or “cluster printing” systems (in which an electronic print job may be split up for distributed higher productivity printing by different marking engines, such as separate printing of the color and monochrome pages). Such integrated printing systems may include a common print media source which supplies print media to each of the marking engines.
In such printing systems, printing on media of varying substrate weight, surface roughness, and coating weight is difficult because the marking engines typically have insufficient latitude to mark and fuse these off-normal substrates at full productivity. Thus the speed of the marking engine is slowed to provide good image quality.
One of the primary limitations encountered when trying to run heavy or coated stock through a xerographic marking engine at high speeds is fusing latitude. Heavy sheets have a larger mass and tend to absorb relatively more heat from the fuser than normal sheets. As a result, the allocation of power to the fusing subsystem of a marking engine can result in the fuser not having sufficient power to handle the high thermal mass materials without experiencing “droop,” the term applied to a drop in fuser roll temperature with time. Typically, single marking engines employ strategies such as “skip pitch” to lower the throughput of the fuser in order to accommodate heavy weight substrate materials. The result is a reduction in the overall efficiency and throughput rate of the machine. In a printing system with multiple marking engines, the throughput of the entire system would be compromised by such a measure and thus use of heavy sheets is avoided.